KR101470334B1 - Method for Preparing Non-woven Fabric Separator Having Improved Mechanical Property and Separator Prepared Using the Same - Google Patents

Abstract

The present invention relates to a method for producing a nonwoven fabric separator for a secondary battery, comprising the steps of: (i) heat treating a nonwoven fabric separator; And (ii) applying pressure to the heat-treated nonwoven fabric separating membrane. The nonwoven fabric separating membrane and the nonwoven fabric separating membrane manufactured by the manufacturing method are provided.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-woven fabric separator having improved mechanical properties and a non-woven fabric separator using the non-woven fabric separator.

The present invention relates to a method for producing a nonwoven fabric separator having improved mechanical properties, and more particularly, to a method for producing a nonwoven fabric separator which comprises: (i) And (ii) applying pressure to the heat-treated nonwoven fabric separating membrane.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operational potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out, and some are commercialized.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing a lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode coated with an active material on an electrode current collector.

The separator should have stability and resistant to degradation and generally exhibit a high electrolytic conductivity for the components of the battery which are in contact with each other. When the separator is manufactured and processed or used in a cell, It should have sufficient strength to maintain the original shape of the membrane while preventing contact.

Particularly, the lithium secondary battery can provide an excellent storage life and a high energy density as compared with other types of batteries. However, since the reactivity of lithium is very high, if the battery is overheated and thermal runaway occurs, There is a high possibility of causing an explosion. However, the porous polyolefin-based film, which is a separator commonly used in lithium secondary batteries, is shrunk by heat and causes internal short-circuit.

Therefore, there is a great need for a technique that has stability at a high temperature and can improve the stability of a battery against an external impact.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have confirmed that a desired effect can be achieved when a battery is manufactured through a process of heat treatment and pressure application of a nonwoven fabric separator as described later , Thereby completing the present invention.

Accordingly, the present invention provides a method for producing a nonwoven fabric separator for a secondary battery, comprising the steps of: (i) heat treating a nonwoven fabric separator; And (ii) applying pressure to the heat-treated nonwoven fabric separating membrane.

More specifically, the nonwoven fabric separating membrane includes pores having a major axis of pores (maximum diameter of pores) of 0.1 to 70 μm using microfine fibers having an average thickness of 0.5 to 10 μm, more specifically, 1 to 7 μm As shown in Fig. It is difficult to manufacture nonwoven fabrics having many pores having a long diameter of less than 0.1 μm, and when the long diameter of the pores exceeds 70 μm, there may arise a problem of lowering the insulating property due to the pore size. The thickness of the nonwoven fabric separator is preferably 5 to 300 μm.

The material of the nonwoven fabric separator may be selected from the group consisting of polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride fluoride: PVdF), and polyvinylchloride (PVC). In some cases, the nonwoven fabric separating film may be formed by using fibers made of two or more materials.

The heat treatment may be performed within a range of -20 ° C to + 20 ° C of the melting point of the material of the nonwoven fabric separator. In this case, the portion where the nonwoven fabric fibers meet is melted and solidified again to increase the strength. If the heat treatment is performed to an excessively high temperature, the nonwoven fabric separator completely melts and the function of the nonwoven fabric separator becomes insufficient. Conversely, if the temperature is too low, the effect of heat treatment is not obtained.

If pressure is applied, the strength of the nonwoven fabric becomes higher. If the pressure is too small, the desired effect can not be obtained. If the pressure is too large, the wettability, which is the advantage of the nonwoven fabric separator, can not be utilized. .

The present invention provides an electrode assembly comprising a non-woven fabric separating membrane manufactured by the above-described method, and an anode, a cathode, and the non-woven fabric separating film interposed between the anode and the cathode.

The anode is prepared by applying a mixture of a cathode active material, a conductive material and a binder on a cathode current collector, followed by drying and pressing. If necessary, a filler may be further added to the mixture.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); A lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _2-x O ₄ ; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

In one specific example, the cathode active material may be a lithium manganese composite oxide having a spinel structure which is a high-potential oxide represented by the following formula (1).

Li _x M _y Mn _{2 - y} O _{4 - z z} (1)

Wherein 0 < y < 2, 0 z < 0.2,

M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;

A is one or more of an anion of -1 or -2.

In detail, the lithium manganese composite oxide represented by Formula 1 may be a lithium nickel manganese composite oxide represented by Formula 2, and more specifically, LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ .

Li _x Ni _y Mn _2-y O ₄ (2)

In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5.

The conductive material is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is prepared by applying, drying and pressing an anode active material on an anode current collector, and may optionally further include a conductive material, a binder, a filler, and the like as described above.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 &lt; x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide and the like can be used.

In one specific example, the negative electrode active material may be a lithium metal oxide represented by the following formula (3).

Li _a M ' _b O _{4-ca c} (3)

In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;

a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;

c is determined according to the oxidation number in the range of 0? c <0.2;

A is one or more of an anion of -1 or -2.

Specifically, the lithium metal oxide represented by Formula 3 may be a lithium titanium oxide (LTO) represented by the following Formula 4, and specifically, Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O _4, etc. However, there is no particular limitation on the composition and kind of lithium ions capable of intercalating / deintercalating lithium ions, and more specifically, It may be a spinel structure of Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ having a small change and excellent reversibility.

Li _a Ti _b O ₄ (4)

In the above formula, 0.5? A? 3, 1? B? 2.5.

Since the lithium titanium oxide (LTO) is required to be dried at a high temperature in order to remove moisture, the nonwoven fabric separator having excellent high temperature stability is more effective for application to such a battery.

In this case, it is preferable to use the spinel lithium nickel manganese composite oxide of Li _x Ni _y Mn _2-y O ₄ represented by the above formula (2) having a relatively high potential due to the high potential of LTO as the cathode active material.

The present invention provides a secondary battery including the electrode assembly, and more particularly, to a lithium secondary battery.

The lithium secondary battery is manufactured by impregnating the electrode assembly with a lithium salt-containing electrolytic solution.

The electrolyte solution containing the lithium salt is composed of an electrolyte solution and a lithium salt. The electrolyte solution may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte, but is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In one specific _{example, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing non-aqueous electrolyte.

Also, the present invention provides a battery module including the secondary battery as a unit battery, a battery pack including the battery module, and a device including the battery pack.

Specific examples of the device include a power tool which is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

INDUSTRIAL APPLICABILITY As described above, the process for producing a nonwoven fabric separator for a secondary battery according to the present invention makes it possible to use a separator having excellent mechanical properties, thereby improving not only the processability but also the defective occurrence rate of the battery, It has the effect of improving the stability without.

1 is a graph showing experimental results of capacity retention rate and resistance increase rate according to Experimental Example 1. FIG.

Hereinafter, the present invention will be described in more detail with reference to embodiments thereof, but the scope of the present invention is not limited thereto.

&Lt; Example 1 >

Fabrication of Nonwoven Membrane

A nonwoven fabric separator (thickness: 16 탆) made of polypropylene was heat-treated at about ± 20 캜 of the melting point and a pressure of 20 tons was applied to produce a nonwoven fabric separator.

Manufacture of Secondary Battery

A negative electrode active material (Li _1.33 Ti _1.67 O ₄ ), a conductive material (Denka black) and a binder (PVdF) having an average particle diameter (D50) of 8.66 탆 and a specific surface area (BET) of 4.01 m ² / To prepare a negative electrode material mixture. The negative electrode material mixture was coated on a copper foil having a thickness of 20 占 퐉 to a thickness of 200 占 퐉, rolled and dried to prepare a negative electrode.

In addition, the positive electrode include LiNi _0.5 Mn _1.5 O ₄ for use as a cathode active material and a conductive material (Denka black), a binder (PVdF), respectively 88.5: 8.5: the after placed in NMP mixed with 3 weight ratio of 20 ㎛ thickness aluminum foil , Rolled and dried to prepare a positive electrode.

An electrode assembly was fabricated between the anode and the cathode thus prepared with the separator (thickness: 20 占 퐉) interposed therebetween. The electrode assembly thus prepared was housed in a pouch-shaped battery case, and then a carbonate-based composite solution containing 1 M of LiPF ₆ was injected into the electrolyte, followed by sealing to assemble the lithium secondary battery.

&Lt; Comparative Example 1 &

A lithium secondary battery was prepared in the same manner as in Example 1, except that the porous separator made of polypropylene having an air permeability of 350 s / ml and a thickness of 16 탆 was used instead of the nonwoven fabric separator as the separator in Example 1, .

<Experimental Example 1>

The secondary battery according to Example 1 and Comparative Example 1 was charged and discharged at 1 C at 2 V to 3.35 V to measure the capacity and discharge resistance. The batteries were stored at 60 ° C. for 4 weeks in an SOC of 100% After that, the capacity and discharge resistance were measured again, and the results are shown in Table 1 and FIG.

1 ^st discharge 60 ° C, 4week, SOC 100% Capacity increase and decrease
(%) Increase / decrease of resistance (%) 1C Capacity (mAh) Discharge resistance
(10s, m) 1C Capacity (mAh) Discharge resistance
(10s, m) Example 1 17.66 2.17 16.34 2.54 92.55 123.93 Comparative Example 1 19.15 1.67 16.35 2.36 85.38 141.77

Referring to Table 1 and FIG. 1, the initial capacity and the resistance performance of the secondary battery of Example 1 were lower than that of the secondary battery of Comparative Example 1. However, in terms of performance deterioration due to high temperature storage, the capacity was maintained at 90% The secondary batteries of Comparative Example 1 exhibited remarkably superior effects compared to Comparative Example 1 in which the rate of increase was as low as 125% or less, the capacity retention rate was about 85%, and the rate of resistance increase was 140% or more.

This means that the nonwoven fabric having a high melting point is improved in mechanical properties through heat treatment, thereby contributing to battery performance, including cell high temperature drying.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (18)

A method for producing a nonwoven fabric separator for a secondary battery,
(i) heat treating the nonwoven fabric separating membrane; And
(ii) applying pressure to the heat-treated nonwoven fabric separator;
/ RTI &gt;
The nonwoven fabric separation membrane may be formed of a material selected from the group consisting of polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride PVdF, polyvinylchloride (PVC), and the like.
Wherein the heat treatment is performed at a temperature ranging from -20 占 폚 to +20 占 폚 of the melting point of the material of the nonwoven fabric separation membrane. delete delete The method for producing a nonwoven fabric separator according to claim 1, wherein the pressure is 10 to 30 tons. A nonwoven fabric separator produced by the method according to any one of claims 1 to 4. An electrode assembly comprising an anode, a cathode, and a separator interposed between the anode and the cathode. The electrode assembly according to claim 6, wherein the anode is a high-voltage anode comprising a lithium manganese composite oxide having a spinel structure represented by the following Formula 1 as a cathode active material:
Li _x M _y Mn _{2 - y} O _{4 - z z} (1)
Wherein 0 < y < 2, 0 z < 0.2,
M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;
A is one or more of an anion of -1 or -2. The electrode assembly according to claim 7, wherein the lithium manganese composite oxide represented by Formula 1 is a lithium nickel manganese complex oxide (LNMO) represented by Formula 2 below:
Li _x Ni _y Mn _2-y O ₄ (2)
In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5. The electrode assembly according to claim 8, wherein the lithium nickel manganese composite oxide (LNMO) of Formula 2 is LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ . The electrode assembly according to claim 6, wherein the cathode comprises a lithium metal oxide represented by the following formula (3) as an anode active material:
Li _a M ' _b O _{4-ca c} (3)
In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;
a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;
c is determined according to the oxidation number in the range of 0? c <0.2;
A is one or more of an anion of -1 or -2. The electrode assembly according to claim 10, wherein the lithium metal oxide represented by Formula 3 is Lithium Titanium Oxide (LTO) represented by Formula 4 below:
Li _a Ti _b O ₄ (4)
In the above formula, 0.5? A? 3, 1? B? 2.5. 12. The electrode assembly of claim 11, wherein the lithium titanium oxide is Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ . A secondary battery comprising the electrode assembly according to claim 6. 14. The secondary battery according to claim 13, wherein the secondary battery is a lithium secondary battery. A battery module comprising a secondary battery according to claim 13 as a unit cell. A battery pack comprising the battery module according to claim 15. A device comprising a battery pack according to claim 16. 18. The device of claim 17, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.

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